In the chemical industry installations are quite common for instance in laboratories or in evaporation installations in which a gaseous or vaporous phase is in contact with a liquid phase. In these installations it is often desirable in case of a sudden pressure drop in the liquid phase to interrupt the access of the other phase to the liquid phase and thus to prevent a pressure drop in the gaseous phase. An example of such installations are, for instance, evaporation installations for radioactive waste waters.
In this latter type of installation the evaporation process is based on the fact that the radioactivity of the waste waters is tied to materials present in solution or undissolved in the water which themselves are not volatile, so that in case of an evaporation they remain in the liquid phase and can there be concentrated. The formed water vapor in the ideal case should contain no radioactivity at all. In practical application there are always more or less drops entrained by the vapor stream which have the same composition as the radioactive liquid which is subjected to vaporization. The carriers of the radioactive activity are thus entrained in the steam drops and during condensation will enter the formed distillate.
If, in these cases, the pressure in the liquid phase of the condenser is subject to a sudden drop, a vigorous steam formation in the evaporator will be the consequence and this will result in high vapor flow speeds and the entrainment of larger amounts of liquid. The distillate then will have an unacceptably high radioactivity.
Analogous problems can arise in various installations in the chemical industry.
It has already been proposed to employ regulating devices in gas or steam ducts which are controlled by the pressure at a specific point of the installation. These prior art devices are, however, not very suitable for the present purpose since in them usually there is a substantial delay in effecting the control action. Besides, there is the difficulty that in case of a power failure the power supply to the control device is likewise interrupted and valuable time may be lost until an emergency power source may be started and the switch-over to such device is effected.
Under a broad aspect the present invention therefore involves the problem to avoid a pressure drop in a system A when the pressure in a system B, for reasons outside the pressure in A is subject to a quick drop. In this case the system A would be filled with a gaseous or vaporous medium under pressure which through an intermediate system A' (which in normal operation is filled with the same medium as the system A at approximately the same pressure) would normally flow into the system B which predominantly is filled with a liquid medium and is under a pressure not dependent on the pressure in the system A. Between the systems A and B there is a pressure equilibrium.
It is therefore the object of the present invention to prevent a sudden pressure drop in the A phase due to an unexpected pressure drop in the liquid phase (phase B).